Positive electrode active material composite particles for lithium ion secondary batteries

Abstract

To provide a positive electrode active material composite particle for a lithium ion secondary battery, with which the energy density per unit volume and the rate characteristics of a lithium ion secondary battery can be effectively enhanced.SOLUTION: Positive electrode active material composite particles for a lithium ion secondary battery are composite particles formed of nanoparticles A which are represented by the following formula (a): LifMngFehM1xPO4...(a) and have an average particle size of 50-150 nm, and nanoparticles B which are represented by the following formula (b): LiM2aMnbO4...(b) and have an average particle size of 50-200 nm, a mass ratio (A:B) of the nanoparticles A and the nanoparticles B being 97:3 to 55:45.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to positive electrode active material composite particles for lithium ion secondary batteries that increase the energy density per unit volume of the lithium ion secondary battery and improve the rate characteristics. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries are used in a wide range of applications, including mobile phones, digital cameras, laptop computers, hybrid vehicles, and electric vehicles. LiMn is a popular cathode material for these batteries due to its high safety and large capacity. x Fe 1-x Particles having an olivine structure, such as lithium manganese phosphate and lithium iron phosphate, are considered promising, and various developments utilizing such particles are being carried out.

[0003] For example, Patent Document 1 discloses a positive electrode for a lithium ion secondary battery in which a positive electrode active material layer is arranged, the positive electrode active material layer being formed of a first layer containing an active material such as lithium manganese oxide and a second layer containing an active material such as LiFePO4, and attempts to improve the discharge rate characteristics. Furthermore, Patent Document 2 discloses an electrode active material having a core formed from a lithium-containing transition metal oxide such as LiMn2O4, and a shell containing lithium metal oxide particles such as lithium manganese iron phosphate and a polymer, thereby improving safety and stability. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-147790 [Patent Document 2] Special Publication No. 2015-503196 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the case of a positive electrode active material having a structure such as that of Patent Documents 1 and 2, in the lithium ion secondary battery obtained, the energy density per unit volume has not yet been sufficiently increased, and there is still room for improvement in order to exhibit excellent rate characteristics.

[0006] Therefore, an object of the present invention is to provide a positive electrode active material composite particle for a lithium ion secondary battery that can effectively increase the energy density per unit volume and the rate characteristics of the lithium ion secondary battery.

Means for Solving the Problems

[0007] Therefore, as a result of intensive studies to solve the above problems, the present inventors have found that lithium manganese iron phosphate nanoparticles and nanoparticles represented by a specific formula such as LiMn2O4 form composite particles while having a specific mass ratio, thereby effectively increasing the energy density per unit volume in a lithium ion secondary battery and also improving the rate characteristics. It has been found that positive electrode active material composite particles for a lithium ion secondary battery can be obtained.

[0008] That is, the present invention provides the following formula (a): Li f Mn g Fe h M 1 x PO4···(a) (In formula (a), M 1 represents one or more elements selected from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. f, g, h, and x satisfy 0 < f ≦ 1.2, 0.3 ≦ g ≦ 1.2, 0.2 ≦ h ≦ 1.2, 0 ≦ x ≦ 0.3, and 3 / 17 ≦ g / h ≦ 13 / 7, and f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 1 ) × x = 3. ) nanoparticles A represented by the formula and having an average particle size of 50 nm to 150 nm, and The following formula (b): LiM 2 a Mn b O4···(b) (In formula (b), M 2 represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b satisfy 0 ≦ a ≦ 0.1, 0 < b ≦ 2, and (valence of M 2 ) × a + (valence of Mn) × b = 7.) Composite particles formed by nanoparticle B represented by and having an average particle diameter of 50 nm to 200 nm, and provide cathode active material composite particles for a lithium-ion secondary battery in which the mass ratio (A:B) of nanoparticle A to nanoparticle B is 97:3 to 55:45.

Effects of the Invention

[0009] According to the cathode active material composite particles for a lithium-ion secondary battery of the present invention, a lithium-ion secondary battery with effectively enhanced rate characteristics as well as energy density per unit volume can be realized.

Modes for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail. The cathode active material for a lithium-ion secondary battery of the present invention is the following formula (a): Li f Mn g Fe h M 1 x PO4···(a) (In formula (a), M 1 represents one or more elements selected from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. f, g, h, and x satisfy 0 < f ≦ 1.2, 0.3 ≦ g ≦ 1.2, 0.2 ≦ h ≦ 1.2, 0 ≦ x ≦ 0.3, and 3 / 17 ≦ g / h ≦ 13 / 7, and f + (valence of Mn) × g + (valence of Fe) × h + (M1 Indicates a number that satisfies (valence of) × x = 3.) Nanoparticle A represented by and having an average particle size of 50 nm to 150 nm, and The following formula (b): LiM 2 a Mn b O4···(b) (In formula (b), M 2 represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b satisfy 0 ≦ a ≦ 0.1, 0 < b ≦ 2, and (valence of M 2 × a + (valence of Mn) × b = 7.) Nanoparticle B represented by and having an average particle size of 50 nm to 200 nm Composite particles formed by The mass ratio (A:B) of nanoparticle A to nanoparticle B is 97:3 to 55:45.)

[0011] Thus, the positive electrode active material composite particles for a lithium ion secondary battery of the present invention are composite particles formed by forming nanoparticles A and nanoparticles B, which are ultrafine particles represented by specific formulas, while maintaining a limited mass ratio. As a result, these nanoparticles A and nanoparticles B aggregate while being closely intertwined, improving the electrode density and the lithium ion conductivity between the particles and the electrolyte. In the obtained lithium ion secondary battery, it is possible to effectively increase the energy density per unit volume and the rate characteristics.)

[0012] Nanoparticle A forming the positive electrode active material composite particles for a lithium ion secondary battery of the present invention has the following formula (a): Li f Mn g Fe h M 1 x PO4···(a) (In formula (a), M 1represents one or more elements selected from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. f, g, h, and x satisfy 0 < f ≤ 1.2, 0.3 ≤ g ≤ 1.2, 0.2 ≤ h ≤ 1.2, 0 ≤ x ≤ 0.3, and 3 / 17 ≤ g / h ≤ 13 / 7, and satisfy f + (valence of Mn) × g + (valence of Fe) × h + (valence of M 1 (valence) × x = 3. ) It is represented by and has an average particle size of 50 nm to 150 nm.

[0013] The nanoparticle A represented by the above formula (a) is an olivine-type lithium transition metal phosphate compound containing at least both manganese (Mn) and iron (Fe) as transition metals, and is a nano-scale ultrafine particle. The positive electrode active material composite particles for a lithium-ion secondary battery of the present invention are formed by the nanoparticles being densely intertwined and combined while maintaining a specific mass ratio between such nanoparticles A and nanoparticles B described later. Therefore, while effectively increasing the energy density per unit volume, the rate characteristics can be improved.

[0014] Regarding the above nanoparticle A, from the viewpoint of the average discharge voltage, for f, 0.6 ≤ f ≤ 1.2 is preferable, 0.65 ≤ f ≤ 1.15 is more preferable, and 0.7 ≤ f ≤ 1.1 is even more preferable. For g, 0.2 ≤ g ≤ 0.6 is preferable, 0.25 ≤ g ≤ 0.55 is more preferable, and 0.3 ≤ g ≤ 0.5 is even more preferable. For h, 0.4 ≤ h ≤ 0.8 is preferable, 0.45 ≤ h ≤ 0.75 is more preferable, and 0.5 ≤ h ≤ 0.7 is even more preferable. For x, 0 ≤ x ≤ 0.2 is preferable, 0 ≤ x ≤ 0.15 is more preferable, and 0 ≤ x ≤ 0.1 is even more preferable. And g / h is the molar ratio of Mn to Fe constituting the so-called nanoparticle A, and 1 / 4 ≤ g / h ≤ 3 / 2 is preferable, 1 / 3 ≤ g / h ≤ 11 / 9 is more preferable, and 3 / 7 ≤ g / h ≤ 1 is even more preferable.

[0015] Specifically, for example, LiMn 0.2 Fe 0.8 PO4, LiMn0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.75 Fe 0.15 Mg 0.1 PO4, LiMn 0.5 Fe 0.5 PO4, etc. Among them, LiMn 0.2 Fe 0.8 PO4, LiMn 0.4 Fe 0.6 PO4 or LiMn 0.6 Fe 0.4 PO4 is preferred.

[0016] The average particle size of the nanoparticles A represented by the above formula (a) is 50 nm to 150 nm, preferably 60 nm to 140 nm, more preferably 70 nm to 130 nm, even more preferably 80 nm to 120 nm, and even more preferably 90 nm to 110 nm, from the viewpoint of effectively promoting the insertion and desorption of lithium ions and from the viewpoint of handling. Here, the "average particle size" of nanoparticles A refers to the average particle size of 100 particles observed with an SEM (JSM-7001F, manufactured by JEOL Ltd.).

[0017] Nanoparticles A may be particles having cellulose nanofiber-derived carbon and / or water-soluble carbon material-derived carbon supported on their surfaces, in order to ensure excellent discharge capacity and further improve rate characteristics. Cellulose nanofibers are the skeletal component that accounts for approximately 50% of all plant cell walls. They are lightweight, high-strength fibers that can be obtained by defibrating the plant fibers that make up these cell walls to nano-size. The fiber diameter of these cellulose nanofibers is 1 nm to 1,000 nm, and they also have good dispersibility in water. Furthermore, the cellulose molecular chains that make up the cellulose nanofibers form a periodic structure of carbon. Therefore, when these cellulose nanofibers are carbonized to form carbon, which is firmly supported on the surface of the nanoparticles A, they form dense composite particles together with the ultrafine nanoparticles B. This effectively suppresses the degradation of the electronic conductive path, effectively increases the energy density per unit volume, and ensures the development of excellent rate characteristics in the resulting battery.

[0018] When carbon derived from cellulose nanofibers is supported on the surface of nanoparticles A, the atomic equivalent amount of carbon derived from the carbonized cellulose nanofibers, i.e., the amount of carbon derived from cellulose nanofibers supported, is preferably 0.1% by mass to 5.0% by mass, more preferably 0.2% by mass to 4.0% by mass, and even more preferably 0.3% by mass to 3.0% by mass, based on 100% by mass of the total amount of nanoparticles A including the amount of carbon supported.

[0019] Like cellulose nanofibers, water-soluble carbon materials are carbonized to form carbon, and when this is supported on the surface of nanoparticles A, like cellulose nanofibers, it effectively suppresses the deterioration of the electronic conductive path, effectively increases the energy density per unit volume, and ensures the expression of excellent rate characteristics in the resulting battery. Examples of such water-soluble carbonaceous materials include one or more selected from sugars, polyols, polyethers, and organic acids. More specifically, examples include monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; polysaccharides such as starch and dextrin; polyols and polyethers such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, butanediol, propanediol, polyvinyl alcohol, and glycerin; and organic acids such as citric acid, tartaric acid, and ascorbic acid. Among these, from the viewpoint of increasing solubility and dispersibility in a solvent and effectively functioning as a carbonaceous material, glucose, fructose, sucrose, and dextrin are preferred, and glucose is more preferred.

[0020] When carbon derived from a water-soluble carbon material is supported on the surface of nanoparticle A, the atomic equivalent amount of carbon derived from the water-soluble carbon material, i.e., the amount of carbon derived from the water-soluble carbon material supported, is preferably more than 0% by mass and not more than 4.0% by mass, more preferably more than 0% by mass and not more than 3.0% by mass, and even more preferably more than 0% by mass and not more than 2.0% by mass, based on 100% by mass of the total amount of nanoparticle A including the amount of carbon supported.

[0021] The cellulose nanofiber-derived carbon and the water-soluble carbon material-derived carbon may be supported in the form of only cellulose nanofiber-derived carbon, only water-soluble carbon material-derived carbon, or both cellulose nanofiber-derived carbon and water-soluble carbon material-derived carbon. Of these, from the viewpoint of efficiently covering the surface of nanoparticles A, it is preferable to support cellulose nanofiber-derived carbon.

[0022] When the surface of nanoparticle A is supported with carbon derived from cellulose nanofibers and carbon derived from a water-soluble carbon material, the sum of the atomic equivalent amount of carbon derived from cellulose nanofibers and the atomic equivalent amount of carbon derived from the water-soluble carbon material, i.e., the total amount of carbon derived from cellulose nanofibers and the total amount of carbon derived from the water-soluble carbon material, is preferably 0.1% by mass to 5.0% by mass, more preferably 0.2% by mass to 4.0% by mass, even more preferably 0.3% by mass to 3.0% by mass, and even more preferably 0.5% by mass to 2.0% by mass, based on the total amount of nanoparticle A (100% by mass) including the amount of carbon supported.

[0023] The atomic equivalent amount (supported amount) of carbon derived from cellulose nanofibers and the atomic equivalent amount (supported amount) of carbon derived from water-soluble carbon materials present in nanoparticle A refer to values ​​determined by measurements using a carbon / sulfur analyzer. Furthermore, when nanoparticles A carry carbon derived from cellulose nanofibers and / or carbon derived from a water-soluble carbon material on their surfaces, the amount of nanoparticles A includes the amount of these carbons carried.

[0024] The nanoparticles A can be obtained, for example, by the following production method. Specifically, the nanoparticles A include the following steps (Ia) to (IIa): (Ia) A step of adding a metal compound including a lithium compound, a manganese compound, and an iron compound, a phosphate compound, and optionally cellulose nanofibers and / or a water-soluble carbon material, and water to obtain a slurry water i, and then subjecting the resulting mixture to a hydrothermal reaction to obtain a slurry water ii. (IIa) A step of filtering the obtained slurry water ii, washing with water, and drying to obtain nanoparticles A. The manufacturing method includes the steps of:

[0025] The above-mentioned step (Ia) is a step in which metal compounds including lithium compounds, manganese compounds, and iron compounds, phosphate compounds, and optionally cellulose nanofibers and / or water-soluble carbon materials, as well as water, are added to obtain slurry water i, which is then subjected to a hydrothermal reaction to obtain slurry water ii. Examples of the lithium compound to be used include hydroxides (for example, LiOH·H2O, LiOH), carbonates, acetates, and nitrates. Of these, hydroxides are preferred. Examples of manganese compounds include manganese acetate, manganese nitrate, and manganese oxide. These may be used alone or in combination of two or more. Among these, manganese oxide is preferred from the viewpoint of improving battery characteristics. In addition to these lithium compounds and manganese compounds, metal compounds other than manganese compounds and iron compounds (M 1 ) compounds may also be used.

[0026] Examples of phosphoric acid compounds include orthophosphoric acid (H3PO4, phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, etc. Among these, phosphoric acid is preferably used, and is preferably used as an aqueous solution with a concentration of 70% by mass to 90% by mass. When carbon derived from cellulose nanofibers and / or carbon derived from a water-soluble carbon material is to be supported on the surface of nanoparticles A, the above-mentioned cellulose nanofibers and / or water-soluble carbon material may be further used.

[0027] The slurry water i may be prepared according to a conventional method by determining the amounts of lithium compounds, metal compounds including manganese compounds and iron compounds, and phosphate compounds, etc., depending on the composition of the desired nanoparticles A.

[0028] The resulting slurry water i is then subjected to a hydrothermal reaction to obtain slurry water ii. The amount of water used in the hydrothermal reaction is preferably 10 mol to 50 mol, and more preferably 12.5 mol to 45 mol, per mol of phosphate ions contained in the slurry water i, from the viewpoints of the solubility of the metal compound, ease of stirring, synthesis efficiency, and the like.

[0029] The hydrothermal reaction may be carried out at a temperature of 100 °C or higher, preferably 130 °C to 200 °C. The hydrothermal reaction is preferably carried out in a pressure-resistant container. When the reaction is carried out at 130 °C to 200 °C, the pressure at this time is preferably 0.3 MPa to 1.6 MPa, and when the reaction is carried out at 140 °C to 160 °C, the pressure is preferably 0.3 MPa to 0.6 MPa. The hydrothermal reaction time is preferably 0.1 hour to 48 hours, more preferably 0.2 hour to 24 hours.

[0030] The above step (IIa) is a step of filtering the obtained slurry water ii, washing with water, and drying to obtain nanoparticle A. As the drying means, freeze drying and vacuum drying are used.

[0031] The nanoparticle B formed by forming the positive electrode active material composite particles for a lithium ion secondary battery of the present invention has the following formula (b): LiM 2 a Mn b O4···(b) (In formula (b), M 2 represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si. a and b are numbers satisfying 0 ≦ a ≦ 0.1, 0 < b ≦ 2, and (valence of M 2 ) × a + (valence of Mn) × b = 7.) It is represented by and has an average particle size of 50 nm to 200 nm.

[0032] The nanoparticle B represented by the above formula (b) is a particle having a spinel structure. Together with the above nanoparticle A, by forming the composite particle of the present invention while maintaining a specific mass ratio of such ultrafine nanoparticle B, the energy density per unit volume can be increased and the rate characteristics can be improved.

[0033] Specific examples of the nanoparticle B represented by the above formula (b) include LiMn2O4, LiNi 0.5 Mn 1.5 O4, LiCoMnO4, LiCrMnO4, LiFeMnO4, LiAlMnO4, LiCu 0.5 Mn 1.5Among them, LiMn2O4 is preferred.

[0034] From the viewpoint of ensuring excellent rate characteristics and ease of handling, the average particle size of the nanoparticles B is 50 nm to 200 nm, preferably 60 nm to 190 nm, more preferably 70 nm to 180 nm, even more preferably 80 nm to 170 nm, and even more preferably 90 nm to 160 nm. Here, the "average particle size" of nanoparticles B means the average particle size of 100 particles observed with an SEM (JSM-7001F, manufactured by JEOL Ltd.).

[0035] The nanoparticles B can be obtained, for example, by the following production method. Specifically, the nanoparticles B include the following steps (Ib) to (IIb): (Ib) A step of mixing a lithium compound and a manganese compound and firing the mixture at a temperature of 250°C to 500°C to obtain preliminary particles b (IIb) A step of calcining the obtained preliminary particles b at a temperature of 500°C to 750°C in a reducing atmosphere or an inert atmosphere to obtain nanoparticles B. The manufacturing method includes the steps of:

[0036] The above (Ib) is a step in which a lithium compound and a manganese compound are mixed and fired at a temperature of 250°C to 500°C to obtain preliminary particles b.

[0037] As the lithium compound, the same compounds as those used for the nanoparticles A can be used, but hydroxides and nitrates are preferred. As the manganese compound, the same one as that used for the nanoparticles A can be used. In addition to these lithium compounds and manganese compounds, metals other than these compounds (M 2 ) compounds may also be used.

[0038] The amounts of these lithium compounds, manganese compounds, etc. used may be determined appropriately depending on the desired composition of nanoparticles B, and may be mixed in accordance with a conventional method.

[0039] Next, preliminary particles b are obtained by firing at a temperature of 250°C to 500°C. In this way, by undergoing a two-stage firing process in which firing is performed at a temperature lower than the firing temperature in step (IIb) and then firing at a high temperature in the subsequent step (IIb), it is possible to obtain ultrafine nanoparticles B with a desired average particle size and a high degree of crystallinity.

[0040] The firing temperature is 250°C to 500°C, preferably 260°C to 490°C, and more preferably 270°C to 480°C. The firing time is preferably 0.2 hours to 24 hours, more preferably 0.5 hours to 15 hours, and even more preferably 1 hour to 12 hours. The firing atmosphere is preferably air.

[0041] The above (IIb) is a step of calcining the preliminary particles b obtained in the step (Ib) at a temperature of 500° C. to 750° C. in a reducing atmosphere or an inert atmosphere to obtain nanoparticles B. The firing temperature is 500° C. to 750° C., preferably 520° C. to 730° C., and more preferably 540° C. to 710° C. The firing time is preferably 12 hours to 36 hours, more preferably 14 hours to 30 hours, and even more preferably 16 hours to 24 hours.

[0042] The positive electrode active material composite particles for a lithium ion secondary battery of the present invention are composite particles formed from nanoparticles A and nanoparticles B. In the positive electrode active material composite particles for a lithium ion secondary battery of the present invention, the mass ratio (A:B) of nanoparticles A to nanoparticles B is 97:3 to 55:45, preferably 95:5 to 56:44, more preferably 93:7 to 58:42, and even more preferably 91:9 to 60:40, from the viewpoint of allowing nanoparticles A and nanoparticles B to be densely entangled and composited, effectively increasing the energy density per unit volume, and improving the rate characteristics.

[0043] The positive electrode active material composite particle for a lithium ion secondary battery of the present invention may contain, in addition to nanoparticles A and nanoparticles B, other particles such as lithium manganese phosphate or lithium iron phosphate, or may be a composite particle formed from nanoparticles A, nanoparticles B, and other particles.

[0044] Specific examples of such lithium manganese phosphate or lithium iron phosphate include LiMnPO4, LiMn 0.9 Mg 0.1 PO4, LiMn 0.97 Zr 0.03 PO4, Li 1.2 Mn 0.9 PO4, Li 0.6 Mn 1.2 PO4, LiFePO4, LiFe 0.9 Mg 0.1 PO4, LiFe 0.97 Zr 0.03 PO4, Li 1.2 Fe 0.9 PO4, Li 0.6 Fe 1.2 PO4, etc. Among these, LiMnPO4 and LiFePO4 are preferred.

[0045] The total amount of nanoparticles A and nanoparticles B in 100% by mass of the positive electrode active material composite particles for lithium ion secondary batteries of the present invention is preferably 95% by mass to 100% by mass, more preferably 96% by mass to 100% by mass, and even more preferably 97% by mass to 100% by mass. The other particles may be contained as the remainder.

[0046] The positive electrode active material composite particles for lithium ion secondary batteries of the present invention have an average particle size of preferably 8 μm to 50 μm, more preferably 9 μm to 40 μm, and even more preferably 9.5 μm to 30 μm, from the viewpoint of effectively increasing the energy density per unit volume and improving the rate characteristics by being composite particles in which nanoparticles A and nanoparticles B are densely combined. Here, the "average particle size" of the positive electrode active material composite particles for a lithium ion secondary battery of the present invention is the D 50 The values ​​are the particle diameters (median diameters) at 50% of the cumulative particle size.

[0047] The positive electrode active material composite particles for lithium ion secondary batteries of the present invention are a fired product of granules containing the above-mentioned nanoparticles A and nanoparticles B in a mass ratio (A:B) of nanoparticles A to nanoparticles B of 97:3 to 55:45. Such positive electrode active material composite particles for lithium ion secondary batteries can be obtained, for example, by the following production method. Specifically, the following steps (Ix) to (IIx): (Ix) A step of adding nanoparticles A, nanoparticles B, and optionally other particles, and water to obtain slurry water i', followed by spray drying to obtain granules X. (IIx) A step of calcining the obtained granules X in a reducing atmosphere or an inert atmosphere to obtain composite particles. The manufacturing method includes the steps of:

[0048] The above-mentioned (Ix) is a step in which nanoparticles A, nanoparticles B, and optionally the other particles, and water are added to obtain a slurry water i', which is then spray-dried to obtain granules X. The amounts of the nanoparticles A and nanoparticles B may be appropriately adjusted so as to satisfy the above-mentioned mass ratio (A:B). The solid content concentration of the slurry water i' is preferably 5% by mass to 30% by mass, and more preferably 5% by mass to 25% by mass.

[0049] In spray drying, the operating conditions may be set appropriately depending on the apparatus used. For example, the treatment conditions for a micromist dryer (MDL-050M manufactured by Fujisaki Electric Co., Ltd.) equipped with a four-fluid nozzle are such that the hot air temperature is preferably 110°C to 300°C, and more preferably 150°C to 250°C. The volume ratio of the supply amount of hot air to the supply amount of slurry water (supply amount of hot air / supply amount of slurry water) is preferably 500 to 10,000, and more preferably 1,000 to 9,000.

[0050] The above step (IIx) is a step of firing the granules X obtained in the above step (Ix) in a reducing atmosphere or an inert atmosphere to obtain the composite particles of the present invention. The firing temperature is preferably 500°C to 750°C, more preferably 550°C to 700°C, and the firing time is preferably 0.3 hours to 3 hours, more preferably 0.5 hours to 2 hours.

[0051] The positive electrode active material composite particles for lithium ion secondary batteries of the present invention can be used as a positive electrode material to construct a lithium ion secondary battery essentially consisting of a positive electrode, a negative electrode, an electrolyte, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte. Specifically, for example, the positive electrode active material composite particles for lithium ion secondary batteries of the present invention are mixed with acetylene black, ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, or the like to prepare a positive electrode slurry, which is then coated on a current collector and press-molded to form a positive electrode. The positive electrode active material composite particles for a lithium ion secondary battery of the present invention are formed from the above-mentioned ultrafine nanoparticles A and ultrafine nanoparticles B, and these nanoparticles A and nanoparticles B are densely combined while maintaining a limited mass ratio, so that a highly useful positive electrode can be obtained that can effectively increase the energy density per unit volume while also effectively improving the rate characteristics.

[0052] The negative electrode is not particularly limited in terms of material composition, and any known material composition can be used as long as it can absorb lithium ions during charging and release them during discharging. For example, lithium metal, graphite, silicon-based materials (Si, SiOx), lithium titanate, or carbon materials such as amorphous carbon can be used. It is preferable to use an electrode formed of an intercalating material capable of electrochemically absorbing and releasing lithium ions, particularly a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination, such as a combination of graphite and silicon-based materials.

[0053] The electrolyte solution is prepared by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent typically used in electrolyte solutions for lithium ion secondary batteries, and examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, and oxolane compounds.

[0054] The supporting salt is not particularly limited in type, but is preferably at least one of inorganic salts selected from LiPF6, LiBF4, LiClO4, and LiAsF6, derivatives of these inorganic salts, organic salts selected from LiSO3CF3, LiC(SO3CF3)2, LiN(SO3CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9), and derivatives of these organic salts.

[0055] The separator serves to electrically insulate the positive and negative electrodes and retain the electrolyte solution, and may be, for example, a porous synthetic resin film, particularly a porous film of a polyolefin polymer (polyethylene, polypropylene).

[0056] The solid electrolyte electrically insulates the positive and negative electrodes and exhibits high lithium ion conductivity. 0.51 Li 0.34 TiO 2.94 , Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 , 50Li4SiO4·50Li3BO3, Li 2.9 PO 3.3 N 0.46 , Li 3.6 Si 0.6 P 0.4 O4, Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75S4, 30Li2S 26B2S3 44LiI, 63Li2S 36SiS2 1Li3PO4, 57Li2S 38SiS2 5Li4SiO4, 70Li2S 30P2S5, 50Li2S 50GeS2, Li7P3S 11 , Li 3.25 P 0.95 Just use S4.

[0057] The shape of the lithium ion secondary battery having the above configuration is not particularly limited, and may be various shapes such as coin-shaped, cylindrical, or rectangular, or may be an irregular shape enclosed in a laminate exterior. [Example]

[0058] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0059] [Production Example 1: Production of Nanoparticles A-1] Slurry water i1 was obtained by mixing 1272 g of LiOH·H2O and 4 L of water. Next, 1153 g of 85% aqueous phosphoric acid solution was added dropwise at 35 mL / min to the resulting slurry water i1 while stirring for 3 minutes at 25 °C. Subsequently, 5892 g of cellulose nanofibers (Wma-10002, manufactured by Sugino Machine, fiber diameter 4-20 nm) were added and stirred at 400 rpm for 12 hours to obtain slurry water i2 containing Li3PO4. The resulting slurry water i2 was purged with nitrogen to adjust the dissolved oxygen concentration of the slurry water i2 to 0.5 mg / L. Then, 482 g of MnSO4·5H2O and 2224 g of FeSO4·7H2O were added to the total amount of slurry water i2' to obtain slurry water i3. The molar ratio of added MnSO4 to FeSO4 (manganese compound:iron compound) was 20:80. The resulting slurry water i3 was then placed in an autoclave and subjected to a hydrothermal reaction at 180°C for 7 hours. The pressure inside the autoclave was 1.0 MPa. After the hydrothermal reaction, the resulting crystals were filtered and washed with 12 parts by mass of water per part by mass of the crystals. The washed crystals were freeze-dried at -50°C for 12 hours to obtain nanoparticles A-1 (LiMn 0.2 Fe0.8 PO4, carbon loading = 1.0 mass%, average particle size: 137 nm) was obtained.

[0060] [Production Example 2: Production of Nanoparticles A-2] Nanoparticles A-2 (LiMn 0.4 Fe 0.6 PO4, carbon loading = 1.1 mass%, average particle size: 106 nm) was obtained.

[0061] [Production Example 3: Production of Nanoparticles A-3] Nanoparticles A-3 (LiMn) were prepared in the same manner as in Production Example 1, except that 5892 g of cellulose nanofibers, 1446 g of MnSO4·5H2O, and 1112 g of FeSO4·7H2O were added, and the hydrothermal reaction was carried out at 140°C for 1 hour. 0.6 Fe 0.4 PO4, carbon loading = 1.0 mass%, average particle size: 62 nm) was obtained.

[0062] [Production Example 4: Production of Nanoparticles A-4] Nanoparticles A-4 (LiMn 0.4 Fe 0.6 PO4, carbon loading = 0.8 mass%, average particle size: 45 nm) was obtained.

[0063] [Production Example 5: Production of Nanoparticles A-5] Nanoparticles A-5 (LiMn 0.1 Fe 0.9 PO4, carbon loading = 1.2 mass%, average particle size: 108 nm) was obtained.

[0064] [Production Example 6: Production of Nanoparticles A-6] Nanoparticles A-6 (LiMn 0.7 Fe 0.3 PO4, carbon loading = 1.0 mass%, average particle size: 109 nm) was obtained.

[0065] [Production Example 7: Production of Nanoparticles B-1] 348 g of manganese dioxide and 84 g of lithium hydroxide monohydrate were mixed and crushed in a ball mill so that the molar ratio of Mn:Li was 2:1, and then calcined at 470°C for 6 hours in an air atmosphere to crush the mixture. Then, calcined at 700°C for 20 hours in an inert atmosphere to obtain particles B-1 (LiMn2O4, average particle size 120 nm).

[0066] [Table 1]

[0067] [Examples 1 and 3, Comparative Examples 3 and 4] According to the formulation shown in Table 2, nanoparticles A and nanoparticles B were each taken out so that the total amount was 1500 g, and 1 L of water was added to each to obtain slurry water i'. 1 The obtained slurry water i' 1 The mixture was dispersed for 1 minute using an ultrasonic agitator (T25, manufactured by IKA) to uniformly color the entire mixture, and then spray-dried using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) (nozzle air flow rate 35 L / min, inlet air temperature 190°C) to obtain granules X. 1 obtained. The obtained granules X 1 The mixture was baked at 700° C. for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain positive electrode active material composite particles.

[0068] [Example 2, Comparative Example 1] According to the formulation shown in Table 2, nanoparticles A and nanoparticles B were each taken out so that the total amount was 1500 g, and 1 L of water was added to each to obtain slurry water i'. 2 The obtained slurry water i' 2 The mixture was dispersed for 1 minute using an ultrasonic agitator (T25, manufactured by IKA) to uniformly color the entire mixture, and then spray-dried using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) (nozzle air flow rate 30 L / min, inlet air temperature 190°C) to obtain granules X. 2 obtained. The obtained granules X 2 The mixture was baked at 700° C. for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain positive electrode active material composite particles.

[0069] [Example 4] According to the formulation shown in Table 2, nanoparticles A and nanoparticles B were each taken out so that the total amount was 1500 g, and 1 L of water was added to each to obtain slurry water i'. 3 The obtained slurry water i' 3 The mixture was dispersed in an ultrasonic agitator (T25, manufactured by IKA) for 1 minute to uniformly color the whole, and then spray-dried (nozzle air flow rate 43 L / min, inlet air temperature 190°C) using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) to obtain granules X. 3 obtained. The obtained granules X 3 The mixture was baked at 700° C. for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain positive electrode active material composite particles.

[0070] [Example 5, Comparative Example 2] According to the formulation shown in Table 2, nanoparticles A and nanoparticles B were each taken out so that the total amount was 1500 g, and 1 L of water was added to each to obtain slurry water i'. 4 The obtained slurry water i' 4 The mixture was dispersed for 1 minute using an ultrasonic agitator (T25, manufactured by IKA) to uniformly color the entire mixture, and then spray-dried using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.) (nozzle air flow rate: 45 L / min, inlet air temperature: 190°C) to obtain granules X.4 obtained. The obtained granules X 4 The mixture was baked at 700° C. for 1 hour in an argon-hydrogen atmosphere (hydrogen concentration 3%) to obtain positive electrode active material composite particles.

[0071] <Evaluation of battery characteristics (rate characteristics)> The resulting positive electrode active materials were used as positive electrode materials to fabricate positive electrodes for lithium-ion secondary batteries. Specifically, the resulting positive electrode active materials, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone was added to the mixture and thoroughly kneaded to prepare a positive electrode slurry. The positive electrode slurry was applied to a 20 μm-thick aluminum foil current collector using a coating machine and vacuum dried at 80°C for 12 hours. The resulting mixture was then punched into a φ14 mm disk and pressed at 16 MPa for 2 minutes using a hand press to form a positive electrode.

[0072] Next, a coin-type secondary battery was constructed using the above positive electrode. A lithium foil punched to a diameter of 15 mm was used as the negative electrode. The electrolyte was a 1 mol / L solution of LiPF6 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7. A polymer porous film was used as the separator. These battery components were assembled and housed in an atmosphere with a dew point of -50°C or lower using standard methods to obtain a coin-type secondary battery (CR-2032).

[0073] Next, using the obtained coin-type secondary battery, the discharge capacity (mAh / g) at 0.2 C (34 mA / g) and 10 C (1.7 A / g) was measured in an environment of 30°C using a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko Corporation), and the rate characteristic value (capacity ratio (%)) was calculated using the following formula (x): Rate Characteristics = [(discharge capacity at 10 C) / (discharge capacity at 0.2 C)] × 100 (x)

[0074] Furthermore, the electrode density was calculated by the following formula (y1), and this was introduced into the following formula (y2) to calculate the energy density per unit volume. Electrode density (g / cm 3 )= Mass of positive electrode active material in the positive electrode (g) / electrode volume (cm 3 )(φ14mm×thickness(μm)) (y1) Energy density per unit volume of positive electrode at 30°C (Wh / L) = Discharge capacity at 30°C (mAh / g) x average voltage (V) x electrode density (g / cm 3 ) (y2) The results are shown in Table 2.

[0075] [Table 2]

Claims

1. The following formula (a): Li f Mn g Fe h M 1 x 2O 4 ・・・(a) (In formula (a), M 1 represents one or more elements selected from Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, and Gd. f, g, h, and x satisfy 0<f≦1.2, 0.3≦g≦1.2, 0.2≦h≦1.2, 0≦x≦0.3, and 3 / 17≦g / h≦13 / 7, and the formula f+(Mn valence)×g+(Fe valence)×h+(Mn valence)×g+(Mn ... 1 (valence of x) × x = 3. Nanoparticles A represented by the formula (I) and having an average particle size of 50 nm to 150 nm; and The following formula (b): LiM 2 a Mn b O 4 ・・・(A) (In formula (b), M 2 represents one or more elements selected from Ni, Co, Al, Mg, Ti, V, Cr, Fe, Zr, Ga, Cu, and Si; a and b are in the range of 0≦a≦0.1, 0<b≦2, and (M 2 (valence of Mn) × a + (valence of Mn) × b = 7. and nanoparticles B having an average particle size of 50 nm to 200 nm A composite particle formed by Positive electrode active material composite particles for lithium ion secondary batteries, in which the mass ratio (A:B) of nanoparticles A to nanoparticles B is 97:3 to 55:

45.

2. 2. The positive electrode active material composite particles for a lithium ion secondary battery according to claim 1, wherein the average particle size is 8 μm to 50 μm.

3. The nanoparticles A have carbon derived from cellulose nanofibers and / or carbon derived from a water-soluble carbon material supported on their surfaces, and 3. The positive electrode active material composite particle for a lithium ion secondary battery according to claim 1, wherein the amount of carbon supported is 0.1% by mass to 5.0% by mass in 100% by mass of the total amount of nanoparticles A.

4. 4. The positive electrode active material composite particle for a lithium ion secondary battery according to claim 1, which is a fired product of a granule containing nanoparticles A and nanoparticles B in a mass ratio (A:B) of nanoparticles A to nanoparticles B of 97:3 to 55:45.

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